Answer :
Final answer:
The total pressure would be the sum of the partial pressures of air and vapor. However, since 'humidity ratio' is typically a dimensionless value, it does not directly contribute to the total pressure. If 'humidity ratio' is indeed referring to a pressure of 0.87 psi, the total pressure would be 1.87 psi, but this usage of terms is unorthodox and the question should be reviewed for clarity.
Explanation:
If the partial pressure of the vapor in a volume of moist air is 1 psi and the humidity ratio is .87, the total pressure of the volume can be calculated. It is important to understand that the humidity ratio, which is also known as the mixing ratio, is the mass of water vapor compared with the mass of dry air. In the context of this question, the term 'humidity ratio' seems to have been used incorrectly, because the humidity ratio is typically a dimensionless quantity and does not contribute directly to total pressure in the manner that partial pressures do.
Dalton's law of partial pressures states that the total pressure in a mixture of gases is equal to the sum of the partial pressures of the individual gases. In this scenario, assuming that the humidity ratio given is actually intended to represent a partial pressure of air (which would be unorthodox and not in line with standard nomenclature), we would simply add the partial pressure of the air to the partial pressure of the vapor to get the total pressure.
Therefore, if the partial pressure of air was somehow also 0.87 psi (though this use of 'humidity ratio' is atypical) and we added it to the vapor pressure of 1 psi, the total pressure would be:
Total pressure = 1 psi (vapor) + 0.87 psi (air) = 1.87 psi
However, without an unambiguous understanding of the standard terms, the calculation above is speculative, and it is recommended to review the question for proper terminology. Typically, the humidity ratio is not used directly in calculating pressures because it is a ratio by mass, not by pressure. If 0.87 is indeed a pressure value in units of psi, the answer would be A. 1.87psi. If not, additional information would be required to answer the question correctly.
